The present invention fits in the agricultural sector and, in particular, in the control of insect plagues detrimental to crops.
More specifically, the present invention provides new emitters of semiochemical substances, with controlled emitting speed, useful for the control of insect plagues in agricultural crops and the process for the preparation thereof.
Insect plagues cause a drastic reduction of crops and insecticides are the traditional method to combat them. However, the use of insecticides has problems such as:
Their toxicity for humans and superior animals, which causes governments to impose more restrictive regulators for the use thereof.
The lack of selectivity, that converts into the destruction of beneficial insects, or of natural predators of the plague that is to be fought
The resistance developed by the insects, which makes it necessary to increase more and more the dosage to maintain the effectiveness thereof.
All of these problems oblige insecticide manufacturers to dedicate more and more resources to R+D in order to obtain better products, but the problem continues to exist.
On its part, society demands respect for the environment but at the same time it requires quality of the agricultural food products, which requires the development of new plague control systems based environmental methods.
It is well known that the communication among insects is basically done by means of a specific type of substances, called xe2x80x9csemiochemical substancesxe2x80x9d (or simply xe2x80x9csemiochemicalsxe2x80x9d), that their organisms naturally emit.
The knowledge of said semiochemical substances as well as the knowledge of the information that the same transmit to the insects permits the development of environmental methods in order to control the behavior of the insects.
In accordance with the above, it is possible to transmit a specific message to a specific species of insects, inducing a specific response by means of the artificial emission of synthetic semiochemicals. Hence, for example, if the message is of attraction, the response of the insect will be directed towards the emitter.
Taking advantage of this inducing capacity the behavior of insects, techniques that permit the control thereof have been developed. Hereinafter a summary of the most important ones is going to be made:
Control, whose purpose is to prevent the occurrence of plagues, to follow their development and to confirm their extinction by means of a count of the captures that are produced in traps provided with an emitter of an attracting semiochemical.
Sexual confusion, that seeks to prevent the reproduction of insects by means of the emission of amounts of a semiochemical that saturates the receptor organs of the insect preventing it to find members of its same species and of the opposite sex.
Massive captures, that seek to significantly reduce the insect population, by means of captures, in traps, with an attracting semiochemical. Aside from the attractant, a toxic agent for the insect, a sexual sterilizer, an entomopathogenic microorganism or simply glue where the insect is adhered and dies, may also be placed in the traps.
The low toxicity of semiochemicals, their high specificity (generally, their action is directed towards a single species), the difficult occurrence of resistances and their non-existent polluting impact, represent outstanding advantages in contrast to conventional insecticides.
So that the use of these semiochemical substances is effective it is necessary to have physical supports capable of emitting the semiochemicals in a controlled manner for a sufficient amount of time, in such a way that a concentration in the air capable of cause the desired response in the insect in a continued manner is achieved.
The cited supports must comply with a series of requirements so that their use is effective:
Provide an adequate emitting speed of the semiochemical.
Permit prolonged duration of the emission
Avoid degradation of the semiochemicals
Not produce contaminating residues
Be economical and allow easy application of the semiochemical
Although there is a large variety of emitting supports on the market such as rubber septa (Aldrich Co., UK; The West Co., Pennsylvania; Arthur H. Thomas Co.; Maavit Products, Tel Aviv, Israel), polyethylene pipes (Shin Etsu Chemical Co., Tokyo, Japan), porous plastic laminates (Hercon Lab. Co., New Jersey, USA); capillary fibers (Albany International, Massachusetts, USA), microcapsules (ICI Agrochemicals, Berks, UK), none of these emitting supports comply with all the above mentioned requirements.
Therefore, there is still the need of emitters of semiochemical substances with supports that acceptably satisfy said requirements and, precisely, this has been the purpose that the applicant""s scientific research has sought. This research has allowed the attainment of the present invention.
Just as it is stated in its title, the present invention refers to new emitters of semiochemical substances with a controlled emitting speed, to a process for the preparation thereof and to the applications thereof for the control of insect plagues in agriculture.
The emitters of the present invention, that comprise a support and a semiochemical substance adsorbed in the support, are characterized in that said support is a sepiolite and in that the retaining capacity between said sepiolite and said semiochemical substance is regulated in such a way that a controlled emission kinetics of said semiochemical substance is obtained.
Natural sepiolites are crystalline magnesium silicates. Structurally, they are formed in laminae of silica tetrahedrons connected by Mg2+ cations, in octahedral coordination (see FIG. 1). The laminae form fibers of a length between 0.5 and 1.5xcexc and in turn, the fibers are connected together by means of Sixe2x80x94Oxe2x80x94Si bridges and carbonates, forming beams with a thickness of about 200 xc3x85
The specific surface of natural sepiolite is around 200-300 m2/g, and can be modified to values between 80 and 600 m2/g (according to the B.E.T. method) by means of adequate treatments, wherein the Sixe2x80x94Oxe2x80x94Si bridges are broken.
The size of the channel of natural sepiolite is relatively small and there is a high polarity inside it, caused by the water from crystallization and the end hydroxyl groups.
Due to this, the regular molecules of semiochemicals have difficulties in entering inside the channels, due to the size thereof and the lack of polarity, and consequently, the adsorption to the sepiolite support is superficial, in most of the cases.
The retaining capacity between the sepiolite and the semiochemical can be carried out from two aspects:
1.xe2x80x94Modification of the sepiolite
2.xe2x80x94Modification of the degree of compacting between the sepiolite and the adsorbed semiochemical.
Within the first group of modifications the following ones can be mentioned:
Modification of the surface cations of the sepiolite
Modification of the specific surface of the sepiolite
Within the second group of modifications the following ones can be mentioned:
Modification of the compacting pressure
Modification of the surface/weight ratio of the finally obtained form
Each one of these modifications will now be analyzed in a more detailed manner.
1. The modification of the surface cations of the sepiolite allows modification of the number of adsorption centers and the retaining force of the semiochemical on the part of the same. An illustrative example of this fact is constituted by the use of different sepiolites modified superficially wherein a specific percentage of surface octahedral magnesium has been replaced by mono or bivalent cations of groups IA and IIA or by protons. The modification of the surface cations of the sepiolite can be done by treatment of the natural sepiolite with acids (for example, sulfuric acid) or with bases (for example, sodium hydroxide).
2. The modification of the specific surface of the sepiolite is especially interesting, taking into account that the fixation of the molecules of semiochemical molecules to the first adsorption layer is much greater than the fixation that is produced in the second and successive layers. Upon increasing the adsorption surface of the sepiolite support, an increase of retention of the semiochemical is produced.
The modification of the specific surface is carried out by means of treatments similar to those indicated in item one above. Specific surface values between 80 and 600 m2/g can be achieved.
3. The modification of the compacting pressure during the manufacturing of the emitter makes it possible to act on the emitting speed. Hence, the greater the pressure at which the sepiolite is compacted with the semiochemical the greater the retention thereof on the support is, thus reducing the emitting speed. On the contrary, a compacting of both products at a lower pressure increases the emitting speed of the semiochemical. The range of compacting pressures is preferably between 0.1 and 20 T/cm2, the pressure being chosen in terms of the needs of emission of the active substance.
4. The modification of the surface/weight ratio of the finally obtained emitting product also makes it possible to act on the emitting speed of the semiochemical. Hence, upon increasing the surface/weight ratio the emitting speed increases; on the contrary, upon reducing said ratio, the emitting speed reduces.
In accordance with the above, for the preparation of the emitters of the present invention one or several gradual modifications of the different physico-chemical variables mentioned in the above paragraphs can be made in order to adapt the sepiolite supports to the characteristics of the semiochemicals and to the specific needs of each emission kinetics for the treatment sought.
The emitters of the present invention can be prepared by associating the support and the semiochemical substance by conventional techniques such as agglomeration, pressing, drying by pulverization and the like, where binding components may or may not be used.
For example, the sepiolitic material can be impregnated, by adding to said powdered material a solution of semiochemical substance, trimedlure, in dichloromethane in a proportion of 1-20 ml of dichloromethane per gram of sepiolite+trimedlure, subsequently eliminating the dichloromethane.
The emitter thus obtained may be applied in the form of powder, wettable powder, granulate, pastilles, or conglomerates with any geometric shape that is desired. Likewise, they may be applied manually or by using any conventional mechanical device.
Preferably, the proportion of semiochemical substance/sepiolite is between 1 and 800 mg. Of semiochemical substance per gram of sepiolite, the proportion being chosen in terms of the needs of emission.
The emitters of semiochemical substances of the present invention are especially useful in order to treat insect plagues in the agricultural sector, either by population control techniques, massive captures, sexual confusion or any other type of attracticide traps, producing sterilizing actions in the insects, insecticides or hormone production inhibitors, among others.
In accordance with the above, the present invention provides new emitters of semiochemical substances that permit controlled and durable emission of the semiochemicals used in the environmental fight against agricultural plagues, with noteworthy advantages in comparison to the emitters developed up to now. Among said advantages the following ones can be emphasized:
The adaptation to the emitting needs and to the properties of each semiochemical.
The capacity to attain high useful life times
The non-existent pollution that they produce, since due to their chemical nature, they blend in the agricultural soil
Their ease of application since they can be used in pastille, granulate or powder form.
The possibility of compacting them with different shapes in order to adapt them to any support.